2011

Table Of Contents
Understand the World and User Coordinate Systems
There are two coordinate systems: a fixed system called the world coordinate
system (WCS) and a movable system called the user coordinate system (UCS).
By default, these two systems are coincident in a new drawing.
Normally in 2D views, the WCS X axis is horizontal and the Y axis is vertical.
The WCS origin is where the X and Y axes intersect (0,0). All objects in a drawing
file are defined by their WCS coordinates. However, it is usually more
convenient to create and edit objects based on the movable UCS.
Work with the User Coordinate System
Virtually all coordinate entry as well as many other tools and operations
reference the current UCS. 2D tools and operations that depend on the location
and orientation of the UCS include the following:
Absolute and relative coordinate entry
Absolute reference angles
Definition of horizontal and vertical for Ortho mode, polar tracking, object
snap tracking, grid display, and grid snap
Orientation of horizontal and vertical dimensions
Orientation of text objects
View rotation using the PLAN command
Moving or rotating the UCS can make it easier to work on particular areas of
a drawing.
You can relocate the user coordinate system with methods such as the
following:
Move the UCS by defining a new origin point.
Align the UCS with an existing object.
Rotate the UCS by specifying a new origin point and a point on the new
X axis.
Rotate the current UCS a specified angle around the Z axis.
Revert to the previous UCS.
Restore the UCS to be coincident with the WCS.
562 | Chapter 17 Use Precision Tools